Graduate College of Marine Studies, Univ. of Delaware, Newark, DE 19716
A mode filtering technique is described and applied to broadband signatures obtained from recent shallow-water acoustic experiments [Badiey et al., J. Acoust. Soc. Am. 96, 3593--3604 (1994)]. The technique uses a combination of a wavelet transform and singular value decomposition. The order of the modes is arranged by means of their respective energy levels. Each energy level is directly associated with the eigenvalues of the decomposed signal. The progressions of modal structures in time and frequency are given for various azimuthal propagation paths. Evolution of modal structure with frequency is examined by measuring the extent of the frequency band for each propagation path. It is shown that the pattern of the modal structure becomes more complicated for higher modes. Furthermore, from the time-frequency analysis, it can be seen that the existence of a given mode can vary with time and that the medium filters the broadband signal. The mode shape is shown as a function of time, frequency, azimuth, sound speed in the sediment, and other shallow-water waveguide parameters.